Systems, devices and methods for neurostimulation having a modulation of packets

ABSTRACT

A method of neurostimulation may include delivering an electrical signal to a plurality of electrodes connected to a patient. The electrical signal may include a plurality of spaced-apart packets of electrical pulses. The method may include modulating at least one of a quantity of the plurality of electrical pulses within ones of the plurality of packets of electrical pulses, a width in time of the plurality of electrical pulses within ones of the plurality of packets of electrical pulses, an amplitude in voltage of the plurality of electrical pulses within ones of the plurality of packets of electrical pulses, a separation in time between adjacent ones of the plurality of electrical pulses within ones of the plurality of packets of electrical pulses, and a separation in time between adjacent ones of the plurality of packets of electrical pulses to modulate the electrical signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Non-Provisional patentapplication Ser. No. 15/757,098, filed Mar. 2, 2018, which is a nationalstage application of PCT Application No PCT/US2016/049824, filed Sep. 1,2016, which in turn claims priority to U.S. Provisional PatentApplication No. 62/322,985, filed Apr. 15, 2016, and U.S. ProvisionalPatent Application No. 62/214,474, filed Sep. 4, 2015, the entirecontents of each of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to neurostimulation, and in particular, toneurostimulation systems, devices, and methods.

BACKGROUND

Neurostimulation is the therapeutic and/or diagnostic activation of oneor more parts of the nervous system. The nervous system may beelectrically stimulated through invasive means, such as implantableelectrodes, or though less invasive means, such as electrodes attachedto the skin. Non-electrical forms of neurostimulation may employelectromagnetic waves, light, sound, or temperature to stimulate thenervous system. Neurostimulation has been used for the purpose ofmedical treatment and/or diagnosis of various disorders.

Vestibular stimulation is a form of neurostimulation that stimulates thevestibular branch of the vestibulocochlear nerve, the eighth cranialnerve. As used herein, “vestibular nerve” shall refer to the vestibularbranch of the eighth cranial nerve. The vestibular nerve may bestimulated electrically, termed Galvanic Vestibular Stimulation (“GVS”),or may be stimulated using temperature, termed Caloric VestibularStimulation.

Some conventional two-pole GVS systems provide an electrical currentbetween the left and right mastoid bones, adjacent to the mastoidprocesses, to pass through the vestibular organs in the inner ear. Someconventional three-pole GVS systems provide electrical currents betweenthe forehead and the left and right mastoids. In order to overcome theelectrical impedance of the skin, the skin may be abraded, a conductivegel may be used, and/or a higher voltage may be used to provide thedesired electrical current. See, e.g., R. C. Fitzpatrick, B. L. Day,Probing the human vestibular system with galvanic stimulation. J ApplPhysiol 96, 2301-2316 (2004); published online EpubJun(10.1152/japplphysiol.00008.2004).

Accordingly, apparatuses and associated methods useful for deliveringlower voltage stimulation to the nervous system and/or the vestibularsystem of an individual are potentially beneficial to take fulladvantage of physiological responses that are useful in diagnosingand/or treating a variety of medical conditions.

SUMMARY OF EMBODIMENTS OF THE INVENTION

In some embodiments, methods of neurostimulation are provided. A methodmay include delivering an electrical signal to a plurality of electrodesconnected to a patient. The electrical signal may include a plurality ofspaced-apart packets of electrical pulses. Ones of the plurality ofpackets may include a plurality of electrical pulses and a separation intime between adjacent ones of the plurality of packets of electricalpulses. Ones of the electrical pulses may include a width in time, anamplitude in voltage and/or current, and a separation in time betweenadjacent ones of the electrical pulses within a packet. The method mayinclude modulating at least one of a quantity of the plurality ofelectrical pulses within ones of the plurality of packets of electricalpulses, the width in time of the plurality of electrical pulses withinones of the plurality of packets of electrical pulses, the amplitude involtage of the plurality of electrical pulses within ones of theplurality of packets of electrical pulses, the separation in timebetween adjacent ones of the plurality of electrical pulses within onesof the plurality of packets of electrical pulses, and the separation intime between adjacent ones of the plurality of packets of electricalpulses to modulate the electrical signal.

In some embodiments, the method may include modulating a quantity of theplurality of electrical pulses within ones of the plurality of packetsof electrical pulses based on a target stimulus frequency.

In some embodiments, the modulating may include modulating the width intime of the plurality of electrical pulses within ones of the pluralityof packets of electrical pulses based on a target stimulus frequency.

In some embodiments, the modulating may include modulating the amplitudein voltage of the plurality of electrical pulses within ones of theplurality of packets of electrical pulses based on a target stimulusfrequency.

In some embodiments, the modulating may include modulating theseparation in time between adjacent ones of the plurality of electricalpulses within ones of the plurality of packets of electrical pulsesbased on a target stimulus frequency.

In some embodiments, the modulating may include modulating theseparation in time between adjacent ones of the plurality of packets ofelectrical pulses based on a target stimulus frequency.

In some embodiments, the modulating may include varying the separationin time between adjacent ones of the plurality of packets of electricalpulses in a sinusoidal modulation between a minimum value and a maximumvalue based on the target stimulus frequency.

In some embodiments, the minimum value of the separation in time betweenadjacent ones of the plurality of packets of electrical pulses may besufficiently large to allow target neurons to recover before beingactivated by the next packet of electrical pulses.

In some embodiments, the varying may include varying the separation intime between adjacent ones of the plurality of packets of electricalpulses according to the formula S(t)=S_(min)+S_(c)*sin(ωt), wherein S(t)is the separation in time between adjacent ones of the plurality ofpackets of electrical pulses, S_(min) and S_(c) are time constants, andω is proportional to the target stimulus frequency.

In some embodiments, the quantity of the plurality of electrical pulseswithin ones of the plurality of packets of electrical pulses may bebetween 2 and about 200. The width in time of the plurality ofelectrical pulses within ones of the plurality of packets of electricalpulses may be between about 10 microseconds and about 500 microseconds.The amplitude in voltage of the plurality of electrical pulses withinones of the plurality of packets of electrical pulses may be betweenabout 1 volt and about 10 volts. The separation in time between adjacentones of the plurality of electrical pulses within ones of the pluralityof packets of electrical pulses may be between about 10 microseconds andabout 500 microseconds.

In some embodiments, the modulating may include varying the separationin time between adjacent ones of the plurality of packets of electricalpulses in a sinusoidal modulation between about 100 microseconds andabout 100 milliseconds.

In some embodiments, the target stimulus frequency may be between about0.005 Hz and about 200 Hz.

In some embodiments, the method may include selecting the modulatedelectrical signal to induce brain rhythms in a target portion of thebrain based on the modulated electrical signal.

In some embodiments, the method may include entraining endogenous brainrhythms in a target portion of the brain based on the modulatedelectrical signal.

In some embodiments, the modulating may include modulating the targetstimulus frequency between a lower target frequency and a higher targetfrequency.

In some embodiments, modulating the target stimulus frequency mayinclude repeatedly increasing and/or decreasing the target stimulusfrequency in a time varying pattern between the lower target frequencyand the higher target frequency.

In some embodiments, modulating the target stimulus frequency mayinclude repeatedly cycling the target stimulus frequency in a pattern ofincreasing from the lower target frequency to the higher targetfrequency and then decreasing back to the lower target frequency.

In some embodiments, delivering the electrical signal may includetransdermal electrical stimulation.

In some embodiments, delivering the modulated electrical signal mayinclude galvanic vestibular stimulation (GVS).

In some embodiments, the method may include delivering a time varyingthermal waveform to the patient through caloric vestibular stimulation(CVS) simultaneous with the delivery of the modulated electrical signalthrough GVS.

In some embodiments, a target stimulus frequency of the GVS may bebetween about 0.005 Hz and about 200 Hz. The GVS may enhance a deliveryof the CVS to a target portion of the brain.

In some embodiments, the modulation of the electrical signal may includemodulating the electrical signal based on a modulation waveform. In someembodiments, the modulation waveform may include an audio waveform. Insome embodiments, the audio waveform may include music. In someembodiments, the audio waveform may include voice.

In some embodiments, the method may include acoustically delivering anaudio waveform to the patient simultaneous with the delivery of themodulated electrical signal. In some embodiments, the audio waveform mayinclude music. In some embodiments, the audio waveform may includevoice. In some embodiments, the modulation of the electrical signal maybe based on the audio waveform.

In some embodiments, the electrodes may include earpieces that areconfigured to be inserted in respective ears of the patient. Theearpieces may include speakers that deliver the audio waveform to thepatient. A perceived volume of the delivered audio waveform may indicatethat the earpieces are in sufficient contact with ear canals of thepatient for the modulated electrical signal to be delivered to the earcanals.

In some embodiments, a neurostimulation device is provided. Theneurostimulation device may include first and second electrodes and acontroller. The controller may include a waveform generator configuredto deliver a modulated electrical signal to a subject through the firstand second electrodes. The modulated electrical signal may include aplurality of spaced-apart packets of electrical pulses. Ones of theplurality of packets may include a plurality of electrical pulses and aseparation in time between adjacent ones of the plurality of packets ofelectrical pulses. Ones of the electrical pulses may include a width intime, an amplitude in voltage, and a separation in time between adjacentones of the electrical pulses within a packet. At least one of aquantity of the plurality of electrical pulses within ones of theplurality of packets of electrical pulses, the width in time of theplurality of electrical pulses within ones of the plurality of packetsof electrical pulses, the amplitude in voltage of the plurality ofelectrical pulses within ones of the plurality of packets of electricalpulses, the separation in time between adjacent ones of the plurality ofelectrical pulses within ones of the plurality of packets of electricalpulses, and the separation in time between adjacent ones of theplurality of packets of electrical pulses may be modulated to modulatethe electrical signal.

In some embodiments, the first and second electrodes may be configuredto deliver the modulated electrical signal to the subject throughtransdermal electrical stimulation.

In some embodiments, the neurostimulation device may include first andsecond earpieces. Each of the earpieces may include a respective one ofthe first and second electrodes. Ones of the first and second electrodesmay be configured to be insertable into a respective ear canal of thesubject and configured to deliver the modulated electrical signal to thesubject through galvanic vestibular stimulation (GVS).

In some embodiments, the controller may be configured to modulate theseparation in time between adjacent ones of the plurality of packets ofelectrical pulses based on a target stimulus frequency.

In some embodiments, the controller may be configured to vary theseparation in time between adjacent ones of the plurality of packets ofelectrical pulses in a sinusoidal modulation between a minimum value anda maximum value based on the target stimulus frequency.

In some embodiments, the minimum value of the separation in time betweenadjacent ones of the plurality of packets of electrical pulses may besufficiently large to allow target neurons to recover before beingactivated by the next packet of electrical pulses.

In some embodiments, the controller may be configured to modulate theseparation in time between adjacent ones of the plurality of packets ofelectrical pulses according to the formula S(t)=S_(min)+S_(c)*sin(ωt),wherein S(t) is the separation in time between adjacent ones of theplurality of packets of electrical pulses, S_(min) and S_(c) are timeconstants, and ω is proportional to the target stimulus frequency.

In some embodiments, the quantity of the plurality of electrical pulseswithin ones of the plurality of packets of electrical pulses may bebetween 2 and about 200. The width in time of the plurality ofelectrical pulses within ones of the plurality of packets of electricalpulses may be between about 10 microseconds and about 500 microseconds.The amplitude in voltage of the plurality of electrical pulses withinones of the plurality of packets of electrical pulses may be betweenabout 1 volt and about 10 volts. The separation in time between adjacentones of the plurality of electrical pulses within ones of the pluralityof packets of electrical pulses may be between about 10 microseconds andabout 500 microseconds.

In some embodiments, a minimum value of the separation in time betweenadjacent ones of the plurality of packets of electrical pulses may begreater than about 100 microseconds. A maximum value of the separationin time between adjacent ones of the plurality of packets of electricalpulses may be less than about 100 milliseconds.

In some embodiments, the target stimulus frequency may be between about0.005 Hz and about 200 Hz.

In some embodiments, the modulated electrical signal may be configuredto induce brain rhythms in a target portion of a brain of the subjectbased on the target stimulus frequency.

In some embodiments, the modulated electrical signal may be configuredto entrain endogenous brain rhythms in a target portion of a brain ofthe subject based on the target stimulus frequency.

In some embodiments, controller may be configured to modulate the targetstimulus frequency between a lower target frequency and a higher targetfrequency.

In some embodiments, the controller may be configured to repeatedlyincrease and/or decrease the target stimulus frequency in a patternbetween the lower target frequency and the higher target frequency.

In some embodiments, the controller may be configured to repeatedlycycle the target stimulus frequency in a pattern of increasing from thelower target frequency to the higher target frequency and thendecreasing back to the lower target frequency.

In some embodiments, the neurostimulation device may include first andsecond thermoelectric devices thermally coupled to the first and secondearpieces, respectively. The neurostimulation device may include firstand second heat sinks thermally coupled to the first and secondthermoelectric devices, respectfully, opposite the respective one of thefirst and second earpieces. The controller may be configured to generatea first control signal to control a first time varying thermal waveformoutput from the first thermoelectric device and a second control signalto control a second time varying thermal waveform output from the secondthermoelectric device.

In some embodiments, the first and second thermoelectric devices may beconfigured to provide caloric vestibular stimulation (CVS) based on thefirst and second control signals.

In some embodiments, the device may be configured to provide the GVSsimultaneous with the CVS.

In some embodiments, the target stimulus frequency of the GVS may bebetween about 0.005 Hz and about 200 Hz. The GVS may enhance a deliveryof the CVS to a target portion of a brain of the subject.

In some embodiments, the controller may be configured to measure animpedance between the first and second electrodes. The controller may beconfigured to determine that the measured impedance is below athreshold. The threshold may indicate that the earpieces are insufficient contact with the ear canals of the subject for the modulatedelectrical signal to be delivered to the ear canals.

In some embodiments, the controller may be configured to modulate theelectrical signal based on a modulation waveform. In some embodiments,the modulation waveform may include an audio waveform. In someembodiments, the audio waveform may include music. In some embodiments,the audio waveform may include voice.

In some embodiments, the neurostimulation device may include first andsecond speakers. The controller may be configured to acousticallydeliver an audio waveform to the patient via the first and secondspeakers simultaneous with the delivery of the modulated electricalsignal. In some embodiments, the audio waveform may include music. Insome embodiments, the audio waveform may include voice. In someembodiments, the modulation of the electrical signal may be based on theaudio waveform.

In some embodiments, the electrodes may include earpieces that areconfigured to be inserted in respective ears of the patient. A perceivedvolume of the delivered audio waveform may indicate that the earpiecesare in sufficient contact with ear canals of the patient for themodulated electrical signal to be delivered to the ear canals.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention and,together with the description, serve to explain principles of theinvention.

FIG. 1 is a schematic block diagram illustrating stimulation devices,methods, and systems according to some embodiments of the presentinvention;

FIG. 2 is a front view illustrating a stimulation device having in-earelectrodes according to some embodiments of the present invention;

FIG. 3 is a front and side view illustrating a user wearing astimulation device according to some embodiments of the presentinvention;

FIG. 4 is a schematic block diagram illustrating a stimulation deviceaccording to some embodiments of the present invention;

FIGS. 5A and 5B are schematic block diagrams illustrating simulationdevices according to some embodiments of the present invention;

FIG. 6A is a front perspective view illustrating an earpiece of thestimulation device of FIG. 5A;

FIG. 6B is a cross-sectional view schematically illustrating theearpiece of FIG. 6A;

FIG. 7 is a side view illustrating various alternative shapes and sizesof earpieces of stimulation devices according to some embodiments of thepresent invention;

FIG. 8 is a schematic diagram illustrating a path of a stimulationsignal for an externally applied stimulation signal according to someembodiments of the present invention;

FIG. 9 is a cross-sectional view schematically illustrating an ear andsurrounding portions of a human body;

FIG. 10 is a cross-sectional view schematically illustrating relativeplacements of electrodes with respect to a computerized tomography scanof a human head;

FIG. 11 is a graph illustrating a relationship between an impedance ofskin and a frequency of a stimulation waveform according to someembodiments of the present invention;

FIG. 12 is a graph illustrating modulated stimulation waveform accordingto some embodiments of the present invention;

FIG. 13 is a graph illustrating a modulated separation in time betweenadjacent ones of a plurality of packets of electrical pulses accordingto some embodiments of the present invention;

FIG. 14 is a graph illustrating a modulated separation in time betweenadjacent ones of a plurality of packets of electrical pulses and acorresponding modulated stimulation waveform according to someembodiments of the present invention;

FIGS. 15A, 15C, and 15E are graphs illustrating modulated targetstimulus frequencies according to some embodiments of the presentinvention;

FIGS. 15B, 15D, and 15F are graphs illustrating modulated separations intime between adjacent ones of a plurality of packets of electricalpulses according to the modulated target stimulus frequencies of FIGS.15A, 15C, and 15E, respectively.

FIGS. 16A-D are graphs illustrating a method for modulating anelectrical signal according to some embodiments of the presentinvention.

FIG. 17 is a schematic block diagram illustrating portions of acontroller according to some embodiments of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The present invention now will be described hereinafter with referenceto the accompanying drawings and examples, in which embodiments of theinvention are shown. This invention may, however, be embodied in manydifferent forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art.

Like numbers refer to like elements throughout. In the figures, thethickness of certain lines, layers, components, elements or features maybe exaggerated for clarity.

Definitions

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a,” “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, steps, operations, elements, and/orcomponents, but do not preclude the presence or addition of one or moreother features, steps, operations, elements, components, and/or groupsthereof. As used herein, the term “and/or” includes any and allcombinations of one or more of the associated listed items. As usedherein, phrases such as “between X and Y” and “between about X and Y”should be interpreted to include X and Y. As used herein, phrases suchas “between about X and Y” mean “between about X and about Y.” As usedherein, phrases such as “from about X to Y” mean “from about X to aboutY.”

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the specification andrelevant art and should not be interpreted in an idealized or overlyformal sense unless expressly so defined herein. Well-known functions orconstructions may not be described in detail for brevity and/or clarity.

It will be understood that when an element is referred to as being “on,”“attached” to, “connected” to, “coupled” with, “contacting,” etc.,another element, it can be directly on, attached to, connected to,coupled with or contacting the other element or intervening elements mayalso be present. In contrast, when an element is referred to as being,for example, “directly on,” “directly attached” to, “directly connected”to, “directly coupled” with or “directly contacting” another element,there are no intervening elements present. It will also be appreciatedby those of skill in the art that references to a structure or featurethat is disposed “adjacent” another feature may have portions thatoverlap or underlie the adjacent feature.

Spatially relative terms, such as “under,” “below,” “lower,” “over,”“upper” and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is inverted, elements described as “under” or “beneath” otherelements or features would then be oriented “over” the other elements orfeatures. Thus, the exemplary term “under” can encompass both anorientation of “over” and “under.” The device may be otherwise oriented(rotated 90 degrees or at other orientations) and the spatially relativedescriptors used herein interpreted accordingly. Similarly, the terms“upwardly,” “downwardly,” “vertical,” “horizontal” and the like are usedherein for the purpose of explanation only unless specifically indicatedotherwise.

It will be understood that, although the terms “first,” “second,” etc.may be used herein to describe various elements, these elements shouldnot be limited by these terms. These terms are only used to distinguishone element from another. Thus, a “first” element discussed below couldalso be termed a “second” element without departing from the teachingsof the present invention. The sequence of operations (or steps) is notlimited to the order presented in the claims or figures unlessspecifically indicated otherwise.

The present invention is described below with reference to blockdiagrams and/or flowchart illustrations of methods, apparatus (systems)and/or computer program products according to embodiments of theinvention. It is understood that one or more blocks of the blockdiagrams and/or flowchart illustrations, and combinations of blocks inthe block diagrams and/or flowchart illustrations, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general purpose computer, specialpurpose computer, and/or other programmable data processing apparatus toproduce a machine, such that the instructions, which execute via theprocessor of the computer and/or other programmable data processingapparatus, create means for implementing the functions/acts specified inthe block diagrams and/or flowchart block or blocks.

These computer program instructions may also be stored in acomputer-readable memory that can direct a computer or otherprogrammable data processing apparatus to function in a particularmanner, such that the instructions stored in the computer-readablememory produce an article of manufacture including instructions whichimplement the function/act specified in the block diagrams and/orflowchart block or blocks.

The computer program instructions may also be loaded onto a computer orother programmable data processing apparatus to cause a series ofoperational steps to be performed on the computer or other programmableapparatus to produce a computer-implemented process such that theinstructions which execute on the computer or other programmableapparatus provide steps for implementing the functions/acts specified inthe block diagrams and/or flowchart block or blocks.

Accordingly, the present invention may be embodied in hardware and/or insoftware (including firmware, resident software, micro-code, etc.).Furthermore, embodiments of the present invention may take the form of acomputer program product on a computer-usable or computer-readablenon-transient storage medium having computer-usable or computer-readableprogram code embodied in the medium for use by or in connection with aninstruction execution system.

The computer-usable or computer-readable medium may be, for example butnot limited to, an electronic, optical, electromagnetic, infrared, orsemiconductor system, apparatus, or device. More specific examples (anon-exhaustive list) of the computer-readable medium would include thefollowing: an electrical connection having one or more wires, a portablecomputer diskette, a random access memory (RAM), a read-only memory(ROM), an erasable programmable read-only memory (EPROM or Flash memorysuch as an SD card), an optical fiber, and a portable compact discread-only memory (CD-ROM).

As used herein, the term “vestibular system” has the meaning ascribed toit in the medical arts and includes but is not limited to those portionsof the inner ear known as the vestibular apparatus and thevestibulocochlear nerve. The vestibular system, therefore, furtherincludes, but is not limited to, those parts of the brain that processsignals from the vestibulocochlear nerve.

“Treatment,” “treat,” and “treating” refer to reversing, alleviating,reducing the severity of, delaying the onset of, inhibiting the progressof, or preventing a disease or disorder as described herein, or at leastone symptom of a disease or disorder as described herein (e.g., treatingone or more of tremors, bradykinesia, rigidity or postural instabilityassociated with Parkinson's disease; treating one or more of intrusivesymptoms (e.g., dissociative states, flashbacks, intrusive emotions,intrusive memories, nightmares, and night terrors), avoidant symptoms(e.g., avoiding emotions, avoiding relationships, avoidingresponsibility for others, avoiding situations reminiscent of thetraumatic event), hyperarousal symptoms (e.g., exaggerated startlereaction, explosive outbursts, extreme vigilance, irritability, panicsymptoms, sleep disturbance) associated with post-traumatic stressdisorder). In some embodiments, treatment may be administered after oneor more symptoms have developed. In other embodiments, treatment may beadministered in the absence of symptoms. For example, treatment may beadministered to a susceptible individual prior to the onset of symptoms(e.g., in light of a history of symptoms and/or in light of genetic orother susceptibility factors). Treatment may also be continued aftersymptoms have resolved—for example, to prevent or delay theirrecurrence. Treatment may comprise providing neuroprotection, enhancingcognition and/or increasing cognitive reserve. Treatment may be as anadjuvant treatment as further described herein.

“Adjuvant treatment” as described herein refers to a treatment sessionin which the delivery of one or more galvanic and/or caloric waveformsto the vestibular system and/or the nervous system of a patient modifiesthe effect(s) of one or more active agents and/or therapies. Forexample, the delivery of one or more thermal waveforms to the vestibularsystem and/or the nervous system of a patient may enhance theeffectiveness of a pharmaceutical agent (by restoring the therapeuticefficacy of a drug to which the patient had previously becomehabituated, for example). Likewise, the delivery of one or more galvanicand/or caloric waveforms to the vestibular system and/or the nervoussystem of a patient may enhance the effectiveness of counseling orpsychotherapy. In some embodiments, delivery of one or more galvanicand/or caloric waveforms to the vestibular system and/or the nervoussystem of a patient may reduce or eliminate the need for one or moreactive agents and/or therapies. Adjuvant treatments may be effectuatedby delivering one or more galvanic and/or caloric waveforms to thevestibular system and/or the nervous system of a patient prior to,currently with and/or after administration of one or more active agentsand/or therapies.

“Chronic treatment,” “Chronically treating,” or the like refers to atherapeutic treatment carried out at least 2 to 3 times a week (or insome embodiments at least daily) over an extended period of time(typically at least one to two weeks, and in some embodiments at leastone to two months), for as long as required to achieve and/or maintaintherapeutic efficacy for the particular condition or disorder for whichthe treatment is carried out.

“Waveform” or “waveform stimulus” as used herein refers to the galvanicand/or caloric stimulus delivered to a subject through a suitableapparatus to carry out the methods described herein. “Waveform” is notto be confused with “frequency,” the latter term concerning the rate ofdelivery of a particular waveform. The term “waveform” is used herein torefer to one complete cycle thereof, unless additional cycles (of thesame, or different, waveform) are indicated. As discussed further below,time-varying waveforms may be preferred over constant applications incarrying out the present invention.

“Actively controlled waveform” or “actively controlled time-varyingwaveform” as used herein refers to a waveform stimulus in which theintensity of the stimulus is repeatedly adjusted, or substantiallycontinuously adjusted or driven, throughout the treatment session,typically by control circuitry or a controller in response to activefeedback from a suitably situated sensor, so that drift of the stimulusfrom that which is intended for delivery which would otherwise occur dueto patient contact is minimized.

“Packets of electrical pulses” as used herein refers to a series of atleast two electrical pulses, wherein the pulses are separated apart fromeach other in time by a first time period and the last pulse of onepacket is separated apart from the first pulse of the next packet by asecond time period, the second time period being greater than the firsttime period. Although the electrical pulses are illustrated herein as asquare wave, some embodiments of the inventive concept may includesinusoidal, sawtooth, or other suitable waveforms.

“Modulation,” “modulated signal,” or “modulated waveform” as used hereinrefers to varying one or more parameters of a signal or waveform overtime. For example, in a modulated waveform comprising a plurality ofpackets of electrical pulses, one or more parameters may vary from onepacket to another.

Subjects may be treated with the present invention for any reason. Insome embodiments, disorders for which treatment may be carried outinclude, include, but are not limited to, migraine headaches (acute andchronic), depression, anxiety (e.g. as experienced in post-traumaticstress disorder (“PTSD”) or other anxiety disorders), spatial neglect,Parkinson's disease, seizures (e.g., epileptic seizures), diabetes(e.g., type II diabetes), etc.

Headaches that may be treated by the methods and apparatuses of thepresent invention include, but are not limited to, primary headaches(e.g., migraine headaches, tension-type headaches, trigeminal autonomiccephalagias and other primary headaches, such as cough headaches andexertional headaches) and secondary headaches. See, e.g., InternationalHeadache Society Classification ICHD-II.

Migraine headaches that may be treated by the methods and apparatuses ofthe present invention may be acute/chronic and unilateral/bilateral. Themigraine headache may be of any type, including, but not limited to,migraine with aura, migraine without aura, hemiplegic migraine,opthalmoplegic migraine, retinal migraine, basilar artery migraine,abdominal migraine, vestibular migraine and probable migraine. As usedherein, the term “vestibular migraine” refers to migraine withassociated vestibular symptoms, including, but not limited to, headmotion intolerance, unsteadiness, dizziness and vertigo. Vestibularmigraine includes, but is not limited to, those conditions sometimesreferred to as vertigo with migraine, migraine-associated dizziness,migraine-related vestibulopathy, migrainous vertigo and migraine-relatedvertigo. See, e.g., Teggi et al., HEADACHE 49:435-444 (2009).

Tension-type headaches that may be treated by the methods andapparatuses of the present invention, include, but are not limited to,infrequent episodic tension-type headaches, frequent episodictension-type headaches, chronic tension-type headache and probabletension-type headache.

Trigeminal autonomic cephalagias that may be treated by the methods andapparatuses of the present invention, include, but are not limited to,cluster headaches, paroxysmal hemicranias, short-lasting unilateralneuralgiform headache attacks with conjunctival injection and tearingand probable trigeminal autonomic cephalagias. Cluster headache,sometimes referred to as “suicide headache,” is considered differentfrom migraine headache. Cluster headache is a neurological disease thatinvolves, as its most prominent feature, an immense degree of pain.“Cluster” refers to the tendency of these headaches to occurperiodically, with active periods interrupted by spontaneous remissions.The cause of the disease is currently unknown. Cluster headaches affectapproximately 0.1% of the population, and men are more commonly affectedthan women (in contrast to migraine headache, where women are morecommonly affected than men).

Other primary headaches that may be treated by the methods andapparatuses of the present invention, include, but are not limited to,primary cough headache, primary exertional headache, primary headacheassociated with sexual activity, hypnic headache, primary thunderclapheadache, hemicranias continua and new daily-persistent headache.

Additional disorders and conditions that can be treated by the methodsand systems of the present invention include, but are not limited to,neuropathic pain (e.g., migraine headaches), tinnitus, brain injury(acute brain injury, excitotoxic brain injury, traumatic brain injury,etc.), spinal cord injury, body image or integrity disorders (e.g.,spatial neglect), visual intrusive imagery, neuropsychiatric disorders(e.g. depression), bipolar disorder, neurodegenerative disorders (e.g.Parkinson's disease), asthma, dementia, insomnia, stroke, cellularischemia, metabolic disorders, (e.g., diabetes), post-traumatic stressdisorder (“PTSD”), addictive disorders, sensory disorders, motordisorders, and cognitive disorders.

Sensory disorders that may be treated by the methods and apparatuses ofthe present invention include, but are not limited to, vertigo,dizziness, seasickness, travel sickness cybersickness, sensoryprocessing disorder, hyperacusis, fibromyalgia, neuropathic pain(including, but not limited to, complex regional pain syndrome, phantomlimb pain, thalamic pain syndrome, craniofacial pain, cranialneuropathy, autonomic neuropathy, and peripheral neuropathy (including,but not limited to, entrapment-, heredity-, acute inflammatory-,diabetes-, alcoholism-, industrial toxin-, Leprosy-, Epstein BarrVirus-, liver disease-, ischemia-, and drug-induced neuropathy)),numbness, hemianesthesia, and nerve/root plexus disorders (including,but not limited to, traumatic radiculopathies, neoplasticradiculopathies, vaculitis, and radiation plexopathy).

Motor disorders that may be treated by the method and apparatuses of thepresent invention include, but are not limited to, upper motor neurondisorders such as spastic paraplegia, lower motor neuron disorders suchas spinal muscular atrophy and bulbar palsy, combined upper and lowermotor neuron syndromes such as familial amyotrophic lateral sclerosisand primary lateral sclerosis, and movement disorders (including, butnot limited to, Parkinson's disease, tremor, dystonia, TouretteSyndrome, myoclonus, chorea, nystagmus, spasticity, agraphia,dysgraphia, alien limb syndrome, and drug-induced movement disorders).

Cognitive disorders that may be treated by the method and apparatuses ofthe present invention include, but are not limited to, schizophrenia,addiction, anxiety disorders, depression, bipolar disorder, dementia,insomnia, narcolepsy, autism, Alzheimer's disease, anomia, aphasia,dysphasia, parosmia, spatial neglect, attention deficit hyperactivitydisorder, obsessive compulsive disorder, eating disorders, body imagedisorders, body integrity disorders, post-traumatic stress disorder,intrusive imagery disorders, and mutism.

Metabolic disorders that may be treated by the present invention includediabetes (particularly type II diabetes), hypertension, obesity, etc.

Addiction, addictive disorders, or addictive behavior that may betreated by the present invention includes, but is not limited to,alcohol addiction, tobacco or nicotine addiction (e.g., using thepresent invention as a smoking cessation aid), drug addictions (e.g.,opiates, oxycontin, amphetamines, etc.), food addictions (compulsiveeating disorders), etc.

In some embodiments, the subject has two or more of the aboveconditions, and both conditions are treated concurrently with themethods and systems of the invention. For example, a subject with bothdepression and anxiety (e.g., PTSD) can be treated for both,concurrently, with the methods and systems of the present invention.

The methods and systems according to embodiments of the presentinvention utilize galvanic and/or caloric stimulation to inducephysiological and/or psychological responses in a subject for medicallydiagnostic and/or therapeutic purposes. Subjects to be treated and/orstimulated with the methods, devices and systems of the presentinvention include both human subjects and animal subjects. Inparticular, embodiments of the present invention may be used to diagnoseand/or treat mammalian subjects such as cats, dogs, monkeys, etc. formedical research or veterinary purposes.

As noted above, some embodiments according to the present inventionutilize galvanic and/or caloric stimulation to administer stimulation inthe ear canal of the subject. The ear canal serves as a useful conduitto the individual's vestibular system and to the vestibulocochlearnerve. Without wishing to be bound by any particular theory, it isbelieved that galvanic and/or caloric stimulation of the vestibularsystem is translated into electrical stimulation within the centralnervous system (“CNS”) and propagated throughout the brain, includingbut not limited to the brain stem, resulting in certain physiologicalchanges that may be useful in treating various disease states (increasedblood flow, generation of neurotransmitters, etc). See, e.g., Zhang, etal. Chinese Medical J. 121:12:1120 (2008) (demonstrating increasedascorbic acid concentration in response to cold water CVS).

Some embodiments according to the present invention utilize the galvanicand/or caloric stimulation to entrain brain waves at a target frequencyand/or within a target portion of the brain. Brainwave entrainment isany practice that aims to cause brainwave frequencies to fall into stepwith a periodic stimulus having a frequency corresponding to an intendedbrain-state or having a different frequency that induces entrainment bycross frequency coupling. Without wishing to be bound by any particulartheory, it is believed that when the brain is presented with a rhythmicstimulus, the rhythm is reproduced in the brain in the form ofelectrical impulses. If the rhythm resembles the natural internalrhythms of the brain, brainwaves, the brain may respond by synchronizingits own electric cycles to the same rhythm. Examples of entrainmentdescriptors include: phase amplitude coupling, cross frequency coupling,and amplitude-amplitude coupling. The entrained brain waves may continueat the entrained frequency for some time after the stimulus is removed.

Without wishing to be bound by any particular theory, it is currentlybelieved that various brain waves may be entrained by stimulation. Forexample, different subcortical structures may be associated withdifferent frequencies of brain wave modulations. See, e.g., K Omata, THanakawa, M Morimoto, M Honda, Spontaneous Slow Fluctuation of EEG AlphaRhythm Reflects Activity in Deep-Brain Structures: A SimultaneousEEG-fMRI Study. PLoS ONE, vol 8, issue 6, e66869 (June 2013). Therefore,according to some embodiments of the present invention, stimulationfrequencies and/or modulation frequencies may be selected correspondingto a region of the brain for which activation is desired. For example,the selected frequencies may correspond to the frequencies naturallyassociated with a region of the brain. Brain waves may be measured usingelectroencephalogram (EEG). The realization that time-varying signalscould be picked up on the scalp preceded any detailed understanding ofwhat was being recorded. EEG signal results from the collective actionof a region of neurons that fire synchronously. That a voltage can bedetected at all at the scalp is a result of the finite length over whichvoltage differences develop in the cortex (and EEG can only pick upsignals from the cortex). Intraoperatively, there is a method calledECoG (electrocorticography) wherein an electrode array is placeddirectly on the surface of the cortex. This allows for finer scalemeasurements, but may be limited to patients undergoing brain surgery.ECoG generally confirms the findings of EEG in terms of larger-areasynchronous firing. Historically, EEG signals were divided intonon-overlapping frequency bands such that researchers had a commonreference point for brain activity. This approach provided a gross mapof important brain rhythms. For instance, the alpha band (8-13 Hz) maychange a lot (increases power) when the eyes are closed and one focuseson internal thinking versus sensory perception. The gamma band(30-100+Hz) may be associated with global “binding” and may be a markerof unitary thought processes. Brain waves in several bands may beentrained, for example, by listening to music. See, e.g., Doelling, K.B., & Poeppel, D., Cortical entrainment to music and its modulation byexpertise. Proceedings of the National Academy of Sciences, vol 112, no.45, E6233-E6242 (Nov. 10, 2015).

Modulation of brain waves may be used for therapeutic effects. Forexample, non-invasive brain stimulation (NIBS) may improve behavioralperformance in patients that have had a stroke or are suffering fromneuropsychiatric disorders, such as Parkinson's disease (PD) orschizophrenia (SCZ). See, e.g., Krawinkel L K, Engel A K, & Hummel F C,Modulating pathological oscillations by rhythmic non-invasive brainstimulation—a therapeutic concept?, first published online athttp://biorxiv.org/content/early/2015/01/29/014548 (Jan. 29, 2015), alsopublished in Front. Syst. Neurosci. (Mar. 17, 2015). Some disorders,such as PD may be associated with significant alterations inconnectivity between brain regions. See, e.g., Tropinic G, Chiangb J,Wangb Z J, Tya E, & McKeown M J, Altered directional connectivity inParkinson's disease during performance of a visually guided task,Neurolmage, vol. 56, issue 4, 2144-2156 (Jun. 15, 2011). PD patientshave been found to have significantly lower interhemispheric EEGcoherence in various frequencies than healthy control subjects, whichmay impair an ability of the PD patients cognitive and emotionalfunctioning. See, e.g., Yuvaraj R, Murugappan M, Ibrahim N M, SundarajK, Omar M I, Mohamad K, Palaniappan R, & Satiyan M, Inter-hemisphericEEG coherence analysis in Parkinson's disease: Assessing brain activityduring emotion processing, J Neural Transm, 122:237-252 (2015). Some ofthe effects of PD may be improved by the therapeutic use ofneurostimulation. See, e.g., Kim D J, Yogendrakumar V, Chiang J, Ty E,Wang Z J, & McKeown M J, Noisy Galvanic Vestibular Stimulation Modulatesthe Amplitude of EEG Synchrony Patterns, PLoS ONE, vol. 8, issue 7,e69055 (July 2013). Therapeutic neurostimulation may decoupleinter-frequency activity to reduce or reverse abnormalities found inpatients with neuropsychiatric disorders, such as PD. See, e.g., deHemptinne C, Swann N C, Ostrem J L, Ryapolova-Webb E S, San Luciano M,Galifianakis N B, & Starr P A, Therapeutic deep brain stimulationreduces cortical phase-amplitude coupling in Parkinson's disease, NatureNeuroscience, vol. 8, 779-786 (2015).

Aberrant EEG activity has been documented in patients with someneuropsychiatric disorders, such as PD. Non-invasive neuromodulation maybe used to alter EEG. This can take the form of disrupting thedysfunctional rhythm or trying to entrain and thus guide the aberrantrhythm to a “proper” state. Success in achieving neuromodulation may beassessed by, for example, re-measuring EEG activity to see if theabnormal power levels and/or abnormal cross-frequency coupling has beenaddressed. Therefore, according to some embodiments, a therapeuticmethod may include identifying an EEG abnormality and prescribing anassociated therapeutic rhythm. The method may include choosing afrequency range/ranges for neurostimulation, such as with GVS, that maycouple to the abnormal oscillations. The chosen frequency range/rangesmay not be exactly the same as frequencies of the EEG abnormalitybecause cross-frequency coupling can occur. The method may includeadministering the “corrective” GVS stimulation repeatedly over time. Forexample, the administration may continue until the desired change may bemeasured. The desired change may be measured, for example, using EEG ormay be measured using other methods. In some embodiments, the effectsmay be measured by measuring a heart rate variability (HRV).

Some embodiments according to the present invention utilize acombination of galvanic and caloric stimulation. In such embodiments,the galvanic vestibular stimulation may enhance a delivery of thecaloric vestibular stimulation.

As noted above, some embodiments according to the present inventionutilize galvanic stimulation to administer stimulation in the ear canalof the subject. A modulated electrical signal may be transmitted throughthe skin lining the ear canal to stimulate the vestibular system of thesubject. The skin may provide an electrical resistance in the electricalpath between the electrode and the vestibular system. The electricalresistance of the skin may be generally inversely proportional to thefrequency of the electrical signal. Thus, in order to stimulate thevestibular system at lower frequencies, a waveform of larger amplitudemay be required than a waveform at higher frequencies. The largeramplitude may not be desired as the subject may experience discomfort,pain, and/or physical damage based on the large voltage. However, thehigher frequencies may not induce the desired diagnostic and/ortherapeutic effects of galvanic vestibular stimulation. For example,some diagnostic and/or therapeutic uses of galvanic vestibularstimulation desire stimulation at lower frequencies. See, e.g., G. C.Albert, C. M. Cook, F. S. Prato, A. W. Thomas, Deep brain stimulation,vagal nerve stimulation and transcranial stimulation: An overview ofstimulation parameters and neurotransmitter release. Neurosci BiobehavRev 33, 1042-1060 (2009); published online EpubJul(10.1016/j.neubiorev.2009.04.006) (reviewing parameters of stimulationtechniques that explore or treat neurological disorders). In someembodiments of the present invention, a modulation scheme is providedthat generates an electrical signal with a higher frequency to producethe lower impedance and that stimulates the vestibular system at a lowerfrequency.

For example, the modulation scheme may provide a repeating series ofspaced-apart packets of electronic pulses. The electronic pulses withinthe packets may be closely separated in time to provide the higherfrequency and, thus, to produce the lower impedance that permitstransmission through the skin. One or more parameters may be modulatedaccording to a lower frequency. For example, one or more of the quantityof the plurality of pulses within ones of the plurality of packets ofpulses, the width in time of the plurality of electrical pulses withinones of the plurality of packets of pulses, the amplitude of theplurality of pulses within ones of the plurality of packets of pulses,the separation in time between adjacent ones of the plurality of pulseswithin ones of the plurality of packets of pulses, and the separation intime between adjacent ones of the plurality of packets of pulses may bemodulated. The vestibular system may be stimulated based on the lowerfrequency. For example, the lower frequency modulation may entrainbrainwaves based on the low frequency of the modulation. Thus, themodulation scheme may produce the lower impedance based on the higherfrequency of the pulses within a packet and stimulate the vestibularsystem based on the lower frequency of the modulation.

In other embodiments, the modulation scheme may provide an electricalsignal. The electrical signal may include a carrier function thatincludes an amplitude and a carrier frequency. For example, the carrierfunction may be a sine wave. However, in other embodiments the functionmay be another function such as a square wave, sawtooth wave, or anotherfunction. The frequency of the carrier function may be sufficiently highto produce the lower impedance that permits transmission through theskin. One or more parameters of the carrier function may be modulatedaccording to modulation waveform. For example, one or more of theamplitude and frequency of the carrier function may be modulated toproduce a modulated electrical signal. A frequency of the modulationwaveform may be lower than the frequency of the carrier function. Thevestibular system may be stimulated based on the lower frequency. Forexample, the lower frequency modulation may entrain brainwaves based onthe low frequency of the modulation. Thus, the modulation scheme mayproduce the lower impedance based on the higher frequency of the pulseswithin a packet and stimulate the vestibular system based on the lowerfrequency of the modulation.

Some embodiments according to the present invention utilize sound-basedstimulation and/or electronic stimulation based on sounds. Sounds mayaffect brain activity. For example, sounds containing significantquantities of non-stationary high-frequency components (HFCs) above thehuman audible range (approximately 20 kHz) may activate the midbrain anddiencephalon and evoke various physiological, psychological andbehavioral responses. See, e.g., Fukushima A, Yagi R, Kawai N, Honda M,Nishina E, & Oohashi T, Frequencies of Inaudible High-Frequency SoundsDifferentially Affect Brain Activity: Positive and Negative HypersonicEffects, PLoS ONE, vol. 9, issue 4, e95464 (April 2014). Sounds havebeen shown to activate vestibular responses at least up to 2000 Hz. See,e.g., Welgampola M S, Rosengren S M, Halmagyi G M, & Colebatch J G,Vestibular activation by bone conducted sound, J Neurol NeurosurgPsychiatry, 74:771-778 (2003). Without wishing to be bound by anyparticular theory, it is believed that the vestibular response to soundmay be a leftover trait from early evolution when the vestibular systemwas the organ of sound detection when animals lived in the water. Thecochlea developed after animals lived on land and enabled better hearingin the air environment. Since the basic hair cell configuration issimilar in the cochlea and vestibular organs, the basic ability torespond to a range of frequencies may be very similar, if not identical.Since hearing can occur up to approximately 20 KHz in humans, thevestibular system may also respond likewise. Above approximately 1 KhZ,an A.C. component of cochlear response may be dominated by a D.C.response. See, e.g., A. R. Palmer and I. J. Russell, Phase-locking inthe cochlear nerve of the guinea-pig and its relation to the receptorpotential of inner hair-cells, Hearing research, vol. 24, 1-15 at FIG. 9(1986). Therefore, even at the 2000 Hz that has been shown to providevestibular response, the nerve may not be able to follow the stimulussound wave and instead a direct current, DC, offset may occur.

System

FIG. 1 is a schematic block diagram illustrating a stimulation deviceaccording to some embodiments of the present invention. Referring toFIG. 1, a stimulation device 100 may include a controller 110 coupled toelectrodes 115A, 115B. In some embodiments, the controller 110 mayoptionally be also coupled to caloric stimulators 116A, 116B. In someembodiments, the controller 110 may optionally be also coupled tospeakers 117A, 117B. The controller 110 may include a processor 120, I/Ocircuits 140, and/or memory 130. The memory may include an operatingsystem 170, I/O device drivers 175, applications programs 180, and/ordata 190. The application programs 180 may include a waveform generator181 and/or a measurement system 182. The data 190 may include waveformdata 191 and/or measurement data 192. Although illustrated as software,one or more functions of the application programs 180 may be implementedin hardware or in any combination of hardware and/or software.Additionally, it should be understood that one or more functions of thefunctions of the stimulation device 100 may be provided by one or moreseparate devices. For example, one or more portions of the data 190 maybe stored remote from the stimulation device 100.

According to some embodiments of the present invention, the stimulationdevice 100 may stimulate a nervous system by providing first and secondwaveforms to a first electrode 115A and a second electrode 115B. In someembodiments, the first and second waveforms may be modulated electricsignals. In some embodiments, the first and second waveforms may be amodulated voltage level between the electrodes 115A, 115B. In someembodiments, the first and second waveforms may be a modulatedelectrical current between the electrodes 115A, 115B. For example, thefirst and second waveforms may be asymmetric with respect to each otherto provide the modulated voltage level and/or modulated electricalcurrent between the electrodes 115A, 115B. Other embodiments may includeone or more neutral connections to the subject. For example, in someembodiments, the first waveform may be a modulated voltage level betweenthe first electrode 115A and at least one of the neutral connections andthe second waveform may be a modulated voltage level between the secondelectrode 115B and at least one of the neutral connections. In someembodiments, the first waveform may be a modulated electrical currentbetween the first electrode 115A and at least one of the neutralconnections and the second waveform may be a modulated electricalcurrent between the second electrode 115B and at least one of theneutral connections. Thus the electrodes 115A, 115B may be used togetherto provide one stimulus or may be used independently to provide morethan one stimulus.

The controller 110 may generate the first and second waveforms. Thecontroller 110 may include the memory 130, the processor 120 and the I/Ocircuits 140 and may be operatively and communicatively coupled to theelectrodes 115A, 115B. The processor 120 may communicate with the memory130 via an address/data bus 150 and with the I/O circuits 140 via anaddress/data bus 160. As will be appreciated by one of skill in the art,the processor 120 may be any commercially available or custommicroprocessor. The memory 130 may be representative of the overallhierarchy of memory devices containing software and data used toimplement the functionality of the stimulation device 100. Memory 130may include, but is not limited to, the following types of devices:cache, ROM, PROM, EPROM, EEPROM, flash memory, SRAM and DRAM. Memory 130may include non-volatile memory.

As shown in FIG. 1, the memory 130 may comprise several categories ofsoftware and data. For example, the memory may include one or more of:the operating system 170, applications 180, data 190, and input/output(I/O) device drivers 175.

The applications 180 may include one or more programs configured toimplement one or more of the various operations and features accordingto embodiments of the present invention. For example, the applications180 may include the waveform generator 181 configured to communicate awaveform control signal to one or both of the electrodes 115A, 115B. Theapplications 180 may also include the measurement system 182 formeasuring an impedance or other electrical characteristic (e.g.,capacitance) between the electrodes 115A, 115B. In some embodiments, thememory 130 may include additional applications, such as a networkingmodule for connecting to a network. In some embodiments, the waveformgenerator 181 may be configured to activate at least one electrode(i.e., to control the magnitude, duration, waveform and other attributesof stimulation delivered by the at least one electrode). In some suchembodiments, the waveform generator 181 may be configured to activate atleast one electrode based upon a prescription from a prescriptiondatabase, which may include one or more sets of instructions fordelivering one or more time-varying waveforms to the vestibular systemof a subject.

The data 190 may comprise static and/or dynamic data used by theoperating system 170, applications 180, I/O device drivers 175 and/orother software components. The data 190 may include the waveform data191 including one or more treatment protocols or prescriptions. In someembodiments, the data 190 may further include measurement data 192including impedance measurements between the electrodes 115A, 115Band/or estimates of electrical contact based on electrical impedancemeasurements. Electrical impedance measurements may include resistiveand capacitive components of the interface between the electrodes 115A,115B and the ear canal. In some embodiments, the measurement data 192may include measurements of electrical signals that are produced by thevestibular system. For example, the measurement data 192 may includeelectrovestibulography signals, or EVestG signals.

I/O device drivers 175 may include software routines accessed throughthe operating system 170 by the applications 180 to communicate withdevices such as I/O circuits 140, memory 130 components and/or theelectrodes 115A, 115B.

In some embodiments, the waveform generator 181 may be configured topass an electrical current through at least one of the electrodes 115A,115B to stimulate the nervous system and/or the vestibular system of asubject. In particular embodiments, the waveform generator 181 may beconfigured to pass the electrical current through the at least oneelectrode 115A, 115B based upon a prescription comprising a set ofinstructions for delivering one or more time-varying waveforms to thevestibular system of a subject. In some embodiments, the electricalcurrent may be produced in response to an electrical voltagedifferential provided between the two electrodes 115A, 115B. However, insome embodiments, the waveform generator 181 may be configured to passtwo independent electrical currents through the two electrodes 115A,115B, respectively. The two independent electrical currents may beproduced in response to electrical voltage differentials providedbetween each of the two electrodes 115A, 115B and one or more additionalpoints of electrical contact with the body of the subject.

In some embodiments, the stimulation device 100 may be communicativelyconnected to at least one electrode 115A, 115B via a conductive line. Insome embodiments, the stimulation device 100 may be operativelyconnected to a plurality of electrodes, and the stimulation device 100may be operatively connected to each electrode via a separate conductiveline.

In some embodiments, the controller 110 may be operatively connected toat least one of the electrodes 115A, 115B via a wireless connection,such as a Bluetooth connection. In some embodiments, the stimulationdevice 100 may be configured to activate the at least one of theelectrodes 115A, 115B to deliver one or more actively controlled,time-varying waveforms to the vestibular system and/or the nervoussystem of a patient. For example, one or more of the electrodes 115A,115B may be electrically connected to a wireless receiver and a powersource independent of the controller 110. The wireless receiver mayreceive the wireless signal corresponding to a modulated waveform andmay activate the one or more of the electrodes 115A, 115B.

In some embodiments, the stimulation device 100 may include one or morecaloric stimulators, 116A, 116B. The simulation device 100 may stimulatea nervous system by providing third and fourth waveforms to the caloricstimulators, 116A, 116B. The caloric stimulation from the caloricstimulators may be combined with the galvanic stimulation from theelectrodes 115A, 115B.

In some embodiments, the stimulation device 100 may include one or morespeakers, 117A, 117B. The simulation device 100 may provide one or moreaudio waveforms to the speakers, 117A, 117B. In some embodiments, thestimulation device 100 may include an input connector to receive one ormore external audio waveforms that may be provided to the speakers 117A,117B.

FIG. 2 is a front view illustrating a stimulation device according tosome embodiments of the present invention. Referring to FIG. 2, astimulation device 200 may be an in-ear stimulation apparatus. Thestimulation device 200 may be similar to the stimulation device 100illustrated in FIG. 1 except for the differences as noted. Thestimulation device 200 may include a support or headband 230, earphones220, a controller 210 and/or cables 240. In some embodiments, thestimulation device may not include the cables 240 and the controller 210may connect to the earphones 220 wirelessly. The earphones 220 mayinclude respective electrodes 215A, 215B that are configured to bepositioned in the ear of a patient or subject. The electrodes 215A, 215Bmay be configured to make electrical contact with an inner surface ofthe ear of the patient or subject such that, when activated, theelectrode 215A, 215B may stimulate the vestibular system of the patientor subject.

The electrodes 215A, 215B may be configured as respective earpieces250A, 250B or may be configured as parts of the respective earpieces250A, 250B. For example, in some embodiments, an earpiece may be formedprimarily of a conductive metal and the entire earpiece 250A, 250B maybe an electrode 215A, 215B. In other embodiments, a part of or all of anexterior surface of an earpiece 250A, 250B may be coated with anelectrically conductive metal to form the electrode 215A, 215B. In someembodiments, a part of or all of an exterior surface of an earpiece250A, 250B may be coated with an thin layer of an electricallyinsulating material that covers the electrode 215A, 215B andelectrically insulates the electrode 215A, 215B from the ear of thepatient or subject at DC. However, the thin layer of the electricallyinsulating material may allow higher frequency waveforms to pass throughthe thin layer of the electrically insulating material from theelectrode 215A, 215B to the ear of the patient or subject. For example,in some embodiments, the thin layer of the electrically insulatingmaterial may be an anodized finish on an electrically conductive metal.However, in other embodiments, the electrically insulating material maybe a thin layer of rubber, plastic, or another insulating material.

In some embodiments, the electrode 215A, 215B may be in electricalcontact with the ear canal without directly physically contacting theear canal. An electrical conduit may be positioned and configured toprovide or improve electrical contact between the ear canal and theelectrode 215A, 215B. The electrical conduit may be configured toconform to the ear canal, such as a flexible or conformable,electrically conductive material that is configured to increase contactand/or conductivity between the electrode 215A, 215B and the ear canal.The electrically conductive material may be a liquid or solid materialor a combination of liquid and solid materials. Moreover, theelectrically conductive material may be affixed to the electrode 215A,215B. For example, in some embodiments, the electrode 215A, 215B may becovered by a porous material that is permeated with an electricallyconductive liquid. In some embodiments, the electrode 215A, 215B may becovered with a layer of cotton to avoid direct physical contact with theear canal. The layer of cotton may be soaked with an electricallyconductive liquid, for example a saline solution, to provide theelectrical connection between the electrode 215A, 215B and the earcanal. In some embodiments, the electrically conductive liquid may bepositioned in the ear canal. The ear canal may be sealed, for example,with an earplug or other sealing material to contain the electricallyconductive liquid inside the ear canal. In some embodiments theelectrode 215A, 215B and/or an electrical attachment thereto may passthrough or around the earplug or other sealing material.

Although the electrodes 215A, 215B are illustrated in FIG. 2 as beingintegrated with the earpieces 250A, 250B, In some embodiments, theelectrodes 215A, 216B may not be configured to fit within an ear cavity.For example, the electrodes 215A, 216B may be configured to contact aportion of the skin next to the ear and over a mastoid part of atemporal bone.

It should be understood that other configurations for supporting theheadphones and/or earpieces 250A, 250B may be used, including supportbands that are positioned under the chin or over the ear, for example,as may be used with audio earphones. For example, FIG. 3 is a front andside view illustrating a user wearing a stimulation device according tosome embodiments of the present invention. Referring to FIG. 3, astimulation device 200′ may be similar to the stimulation devices 100,200 illustrated in FIGS. 1-2 except for the differences as noted. Thestimulation device 200′ may include straps 260 and/or headbands 270. Insome embodiments, the headbands 270 may provide increased stability ofthe earphones 220 to provide potentially improved contact of theearpieces 250A, 250B (not shown). In some embodiments, one or more ofthe straps 260 and/or headbands 270 may provide an additional point ofelectrical contact to the user, for example a neutral connection to theuser.

Although embodiments according to the present invention are illustratedwith respect to two ear stimulators in which an electric current ispassed from electrode to another through the subject's tissue (e.g., thehead), it should be understood that, in some embodiments, thestimulation device 200′ may only include one electrode 215. In suchembodiments, the stimulation device 200′ may provide an electricalstimulus as a voltage between the electrode 215A and an additional pointof electrical contact. For example, the additional point of electricalcontact may be located on a strap 260 and/or headband 270. In someembodiments, two electrodes 215A, 215B in the ears or on the mastoidsmay be used with one or more additional points of electrical contact topass separate electrical currents from each of the electrodes 215A, 215Bto the one or more additional points of electrical contact.

FIG. 4 is a schematic block diagram illustrating a stimulation deviceaccording to some embodiments of the present invention. Referring toFIG. 4, a stimulation device may be similar to the stimulation devices100, 200 illustrated in FIGS. 1-2 except for the differences as noted.The controller 210 may include a waveform generator 281 and anmeasurement system 282 that may be similar to the waveform generator 181and an measurement system 182 of FIG. 1, except for differences asnoted. The waveform generator 281 may be configured to communicate firstand second waveforms to the electrodes 215A, 215B. It should beunderstood that the first and second waveforms may be the same, or insome embodiments, the first and second waveforms may be different suchthat the output delivered from the electrodes 215A, 215B may beindependently controlled and may be different from one another.

As illustrated in FIG. 4, in some embodiments, the measurement system282 may deliver an electrical current to one or more of the electrodes215A, 215B. In this configuration, the impedance and/or capacitancevalue between the electrodes 215A, 215B may be used to monitor theelectrical contact between the electrodes 215A, 215B. In someembodiments, impedance and/or capacitance values may be detected for arange of subjects to determine a range of impedance and/or capacitancevalues in which it may be assumed that the electrodes 215A, 215B are insufficient electrical contact with the subject's ear canal. When aheadset is being fitted to a new patient, the impedance and/orcapacitance between the electrodes 215A, 215B may be detected, and ifthe impedance value is within the acceptable range, it may be assumedthat there is good electrical contact between the electrodes 215A, 215Band the subject's ear canal.

In some embodiments, when the headset is being fitted to a new patient,the impedance and/or capacitance value between electrodes 215A, 215B maybe detected and used as a patient specific baseline to determine if thepatient is later using the headset and a proper configuration. Forexample, the patient may use a headset according to embodiments of thepresent invention in a setting that may or may not be supervised by amedical professional. In either environment, the measurement system 282may record an impedance and/or capacitance value at a time that is closein time or overlapping with the time in which the treatment waveformsare delivered to the electrodes 215A, 215B. The medical healthprofessional or the measurement system 282 may analyze the impedancevalue to determine whether the electrodes 215A, 215B were properlyfitting during treatment. In some embodiments, the measurement system282 may be configured to provide feedback to the user when impedancevalues detected that are inconsistent with properly fitting electrodes215A, 215B in good electrical contact with the ear canal. In thisconfiguration, the measurement system 282 may provide a degree ofelectrical contact between the electrodes 215A, 215B and the ear canalin real-time or in data recorded and analyzed at a later time.Accordingly, patient compliance with treatment protocols may bemonitored based on the detected impedance during or close in time totreatment.

In some embodiments, the impedance may be calculated based separatelyfor each of the electrodes 215A, 215B. For example, in some embodiments,an impedance may be measured between ones of the electrodes 215A, 215Band an additional point of connection located on a on a strap 240 and/orheadband 270, as illustrated in FIG. 3.

In particular embodiments, the measurement system 282 may also providefeedback to the waveform generator 281, for example, so that thewaveform generator 281 may increase or decrease an amplitude of thewaveform control signal responsive to the degree of electrical contactdetermined by the measurement system 282 based on the impedance and/orcapacitance value. For example, if the measurement system 282 determinesbased on the impedance value that there is a poor fit and poorelectrical contact with the ear canal, then the waveform generator 281may increase an amplitude of the output to the electrodes 215A, 215B tocompensate for the poor electrical contact. In some embodiments, themeasurement system 282 may determine patient compliance, e.g., whetherthe patient was actually using the device during administration of thewaveforms.

Although embodiments of the present invention are illustrated withrespect to two electrodes 215A, 215B, it should be understood that insome embodiments, a single electrode 215A may be used, and an electricalcontact may be affixed to another location on the user's head instead ofthe second earpiece 250B to thereby provide an electrical circuit fordetermining impedance values and estimating thermal contact as describedherein.

In some embodiments, the measurement system 282 may measure one or moreimpedance value based on the current and voltage levels of the first andsecond waveforms. In some embodiments, the measurement system 282 mayinclude hardware to measure the current and/or voltage levels of thefirst and second waveforms. For example, the measurement system 282 maycalculate an impedance by dividing a voltage level by a current level.In such embodiments, the measurement system 282 may calculate animpedance value while the waveform generator 281 generates the first andsecond waveforms.

In some embodiments, the measurement system 282 may measure one or moreelectrical signals that are produced by the vestibular system. Forexample, the measurement system 282 may measure electrovestibulography,or EVestG, signals. EVestG signals may be useful to determine anefficacy of a treatment. For example, EVestG signals may be useful indetermining a presence and/or degree of one or more disorders.Accordingly, an efficacy of a treatment may be monitored based onfeedback provided by the measured EVestG signals during or close in timeto treatment. In some embodiments, a treatment may be revised and/ordiscontinued based on measured EVestG signals.

FIG. 5A is a schematic block diagram illustrating a stimulation deviceaccording to some embodiments of the present invention. Referring toFIG. 5A, a stimulation device 500 may be similar to the stimulationdevice 100 illustrated in FIGS. 1-4 except for the differences as noted.For example, the stimulation device may include a controller 510A andelectrodes 515A, 515B that may be similar to the controller 210 andelectrodes 215A, 215B of FIGS. 1-4, except for differences as noted. Thestimulation device may include earphones including earpieces 550A, 550Bincluding the electrodes 515A, 515B. The earphones may further includethermal electric devices, “TEDs,” attached to the earpieces 550A, 550B.The controller 510A may include a galvanic waveform generator 581A thatmay be similar to the waveform generator 281 of FIGS. 1-4. Thecontroller 510A may also include a caloric waveform generator 581B. Thecaloric waveform generator 518B may be configured to activate the TEDsattached to the earpieces 550A, 550B. In this configuration, caloricvestibular stimulation may be administered to a subject via thesubject's ear canal. Administration of caloric vestibular stimulationusing earpieces is discussed in U.S. patent application Ser. No.12/970,312, filed Dec. 16, 2010, U.S. patent application Ser. No.12/970,347, filed Dec. 16, 2010, U.S. patent application Ser. No.13/525,817, filed Jun. 18, 2012, and U.S. patent application Ser. No.13/994,266, filed May 15, 2014, the disclosures of which are herebyincorporated by reference in their entirety.

In some embodiments, the galvanic waveform generator 581A may deliverfirst and second waveforms to the electrodes 515A, 515B and the caloricwaveform generator may deliver third and fourth waveforms to the TEDsattached to the electrodes 515A, 515B, respectively. In someembodiments, the galvanic waveform generator 581A may deliver first andsecond waveforms and the caloric waveform generator may deliver thirdand fourth waveforms simultaneously. In such embodiments, thestimulation device may deliver galvanic vestibular stimulation andcaloric vestibular stimulation. In some embodiments, the galvanicvestibular stimulation may enhance a delivery of the caloric vestibularstimulation.

FIG. 5B is a schematic block diagram illustrating a stimulation deviceaccording to some embodiments of the present invention. Referring toFIG. 5B, a stimulation device may be similar to the stimulation device100 illustrated in FIGS. 1-4 except for the differences as noted. Forexample, the stimulation device may include a controller 510B andelectrodes 515A, 515B that may be similar to the controller 210 andelectrodes 215A, 215B of FIGS. 1-4, except for differences as noted. Thestimulation device 500 may include earphones including earpieces 550A,550B including the electrodes 515A, 515B. The earphones may furtherinclude speakers attached to the earpieces 550A, 550B. In someembodiments, the speakers may be included in the earpieces, 550A, 515B.In other embodiments, the earpieces 550A, 550B may include a tube orother channel of air that conducts sound from externally attachedspeakers to the inner ear. In yet other embodiments, the stimulationdevice 500 may include bone conduction speakers and the earpieces 550A,550B may conduct vibrations from the bone conduction speakers to bonesthat are adjacent to the ear canals.

In some embodiments, the galvanic waveform generator 581A may deliverfirst and second waveforms to the electrodes 515A, 515B and the audiowaveform generator may deliver audio waveforms to the speakers attachedto the electrodes 515A, 515B, respectively. In some embodiments, thegalvanic waveform generator 581A may deliver first and second waveformsand the audio waveform generator may deliver audio waveformssimultaneously. In such embodiments, the stimulation device 500 maydeliver galvanic vestibular stimulation and audio stimulation. As usedherein, an audio waveform is a waveform that includes frequencycomponents that are within a hearing range of the subject. For example,an audio waveform may include frequency components within a range ofabout 20 to 20,000 Hz. In some embodiments, the audio waveforms may betime-varying and/or may include one or more patterns. For example, theaudio waveforms may include music and/or voice. In some embodiments, thewaveforms of the galvanic vestibular stimulation may be modulated basedon the audio waveforms.

For example, in some embodiments, the first and/or second waveforms ofthe galvanic vestibular stimulation may include a carrier functionhaving a frequency that may be sufficiently high to produce the lowerimpedance that permits transmission through the skin. The audiowaveforms may include one or more frequencies that are lower than thefrequency of the carrier function. One or more parameters of the carrierfunction may be modulated according to the one or more lower frequenciesof the audio waveforms. For example, one or more of the amplitude andfrequency of the carrier function may be modulated to produce the firstand/or second waveforms of the galvanic vestibular stimulation. In otherembodiments, the first and/or second waveforms of the galvanicvestibular stimulation may be directly proportional to the audiowaveforms.

FIG. 6A is a front perspective view illustrating an earpiece of thestimulation device of FIG. 5A. FIG. 6B is a cross-sectional viewschematically illustrating the earpiece of FIG. 6A. Referring to FIGS.6A-6B and FIG. 5A, an earpiece 550 may include an electrode 515. Asnoted above, the electrode 515 may form all, part of, or a coating onthe surface of the earpiece 550. A thermoelectric device 530 may becoupled between the earpiece 550 and a heatsink 540.

The electrode 515 may receive a first or second electrical waveform fromthe galvanic waveform generator 581A of the controller 510A. Theelectrode 515 may be electrically conductive. For example, the electrode515 may be formed of an electrically conductive metal. The electrode 515may be formed to fit in an ear canal and provide an electrical interfaceto the ear canal. Thus, the galvanic waveform generator 581A may providea galvanic stimulus to stimulate the nervous system and/or vestibularsystem of the subject based on the first or second waveform deliveredthrough the electrical connection between the electrode 515 and the earcanal.

In some embodiments, the electrode 515 may be in electrical contact withthe ear canal without directly physically contacting the ear canal. Anelectrical conduit may be positioned and configured to provide orimprove electrical contact between the ear canal and the electrode 515.The electrical conduit may be configured to conform to the ear canal,such as a flexible or conformable, electrically conductive material thatis configured to increase contact and/or conductivity between theelectrode 515 and the ear canal. The electrically conductive materialmay be a liquid or solid material or a combination of liquid and solidmaterials. Moreover, the electrically conductive material may be affixedto the electrode 515. For example, in some embodiments, the electrode515 may be covered by a porous material that is permeated with anelectrically conductive liquid. In some embodiments, the electrode 515may be covered with a layer of cotton to avoid direct physical contactwith the ear canal. The layer of cotton may be soaked with anelectrically conductive liquid, for example a saline solution, toprovide the electrical connection between the electrode 515 and the earcanal. In some embodiments, the electrically conductive liquid may bepositioned in the ear canal. The ear canal may be sealed, for example,with an earplug or other sealing material to contain the electricallyconductive liquid inside the ear canal. In some embodiments theelectrode 515 and/or an electrical attachment thereto may pass throughor around the earplug or other sealing material.

The thermoelectric device 530 may receive a third or fourth thermalwaveform from the caloric waveform generator 581B. The thermoelectricdevice 530 may provide a temperature differential between the earpiece550 and the heatsink 540 based on the third or fourth waveform. Theearpiece 550 and/or the electrode 515 of the earpiece 550 may provide athermal interface between the thermoelectric device 530 and the earcanal. Thus, the caloric waveform generator 581B may provide a caloricstimulus to stimulate the nervous system and/or vestibular system of thesubject based on the third or fourth waveform delivered through thethermal interface between the electrode 515 and the ear canal.

FIG. 7 is a side view illustrating various alternative shapes and sizesof earpieces of stimulation devices according to some embodiments of thepresent invention. Referring to FIG. 7, an earpiece 750 may be similarto the earpieces illustrated in FIGS. 2-6 except for the differences asnoted. A shape and/or size of the earpiece 750 may be selected tooptimize the electrical and/or thermal connection. The shape and/or sizeof the earpiece 750 may be selected for optimal comfort of the subject.In some embodiments, the earpiece 750 may be user replaceable, howeverembodiments of the present invention are not limited thereto. Forexample, in some embodiments, the earpiece 750 may be permanentlyattached to a TED and/or earphone. In some embodiments, a size of theearpiece 750 may be selected according to a size of the ear canal of thesubject. For example, the earpiece 750 may be small, medium, large, orextra large. In some embodiments, a shape of the earpiece 750 may beselected based upon a shape of the ear canal of the subject. Forexample, the earpiece 750 may be angled and/or tortuous (twisted orcurved) with respect to a base of the earpiece 750. However, the presentinvention is not limited to the illustrated shapes and sizes.

FIG. 8 is a schematic diagram illustrating a path of a stimulationsignal according to some embodiments of the present invention. Referringto FIG. 8, a path of a stimulation signal according to some embodimentsof the present invention may include the controller 210, an electrode215, skin, and the vestibular system. The controller 210 may be thecontroller 210 as described above with reference to FIGS. 2-4. Theelectrode 215 may be one or more of the electrodes 215A, 215B, asdescribed above with reference to FIGS. 2-4. The electrode 215 may be inphysical and electrical contact with the skin of a subject. For example,the electrode 215 may be inserted into an ear canal of the subject andmay be in physical and electrical contact with a portion of the skinlining the ear canal of the subject.

FIG. 9 is a cross-sectional view schematically illustrating an ear andsurrounding portions of a human body. Referring to FIG. 9, a vestibularnerve 910 of the vestibular system may be in proximity to an ear canal920. FIG. 10 is a cross-sectional view schematically illustratingrelative placements of electrodes with respect to a computerizedtomography scan of a human head. Referring to FIG. 10, an electrode 1010contacting a portion of the skin lining the ear canal may be in closerproximity to a vestibular nerve 1030 (approximate location shown) thanan electrode 1020 contacting the skin next to the ear and over a mastoidpart of a temporal bone. Referring to FIGS. 8-10, an electrode 215inserted into an ear canal of the subject may be in close proximity to avestibular nerve.

Referring again to FIGS. 8 and 2-4, the waveform generator 281 of thecontroller 210 may electrically stimulate the vestibular system based ona waveform. The waveform may be an electrical signal. The electricalsignal may be modulated. The waveform generator 281 may provide themodulated electrical signal to the electrode 215. In some embodiments,the waveform generator 281 may be electrically connected the electrode215, although the embodiments of the present invention are not limitedthereto. For example, in some embodiments, the waveform generator 281may be wirelessly in communication with an earpiece 250A, 250B that maygenerate and provide the electrical signal to the electrode 215.

The electrode 215 may provide the electrical signal to the vestibularsystem. For example, the electrode 215 may provide the electrical signalto the vestibular system via an electrical connection through the skin.The skin may provide an electrical resistance in the electrical pathbetween the electrode and the vestibular system. Thus, the waveformgenerator 281 may control an amplitude of the waveform such that anamplitude of the electrical signal is sufficient to traverse the skinand stimulate the vestibular system. In some embodiments, the waveformmay be modulated based on a frequency.

FIG. 11 is a graph illustrating a relationship between an impedance ofskin and a frequency of a stimulation waveform according to someembodiments of the present invention. Referring to FIGS. 8 and 11, animpedance of the skin may decrease as a frequency of the waveformincreases. See, e.g., J. Rosell, J. Colominas, P. Riu, R. Pallas-Areny,J. G. Webster, Skin impedance from 1 Hz to 1 MHz, IEEE Trans Biomed Eng35, 649-651 (1988); published online EpubAug (10.1109/10.4599).

For example, at a frequency of 0 Hz, in other words a direct current ofa fixed amplitude, the skin may provide a large impedance in theelectrical path between the electrode and the vestibular system. Thus,in order to stimulate the vestibular system at a frequency of 0 Hz, thewaveform generator 281 may provide a waveform of large amplitude and,accordingly, the electrode may provide an electrical signal with a largevoltage. This may not be desired as the subject may experiencediscomfort, pain, and/or physical damage based on the large voltage.

At higher frequencies, the skin may provide a lower impedance in theelectrical path between the electrode and the vestibular system. Thus,in order to stimulate the vestibular system at higher frequencies, thewaveform generator 281 may provide a waveform of smaller amplitude and,accordingly, the electrode may provide an electrical signal with asmaller voltage. At the lower voltage, the subject may not experiencethe discomfort, pain, and/or physical damage. However, the higherfrequency may not induce the desired diagnostic and/or therapeuticeffects of galvanic vestibular stimulation. For example, some diagnosticand/or therapeutic uses of galvanic vestibular stimulation desirestimulation at a lower frequency. In some embodiments of the presentinvention, a modulation scheme is provided that generates an electricalsignal with a higher frequency to produce the lower impedance and thatstimulates the vestibular system at a lower frequency.

FIG. 17 is a schematic block diagram illustrating portions of acontroller according to some embodiments of the present invention.Referring to FIG. 17, a controller 1710 may be similar to the one ormore of the controllers 210, 510A, 510B of FIGS. 4-5B except for thedifferences as noted. The controller 1710 may include a waveformgenerator 1720 that may generate the modulated electrical signal basedon a modulation waveform. The waveform generator may receive themodulation waveform from a first function generator 1730. The firstfunction generator 1730 may define the modulation waveform and providethe modulation waveform as a modulated voltage to the waveform generator1720. The waveform generator 1720 may include a second functiongenerator 1740. The second function generator 1740 may receive a carrierfunction and the modulation waveform. The second function generator 1740may modulate the carrier function based on the modulation waveform. Forexample, the second function generator 1740 may perform frequencymodulation or amplitude modulation to generate a voltage-based modulatedelectrical signal. In some embodiments, the voltage-based modulatedelectrical signal may be received by a current supply 1750 that producesa clamped current output that may be provided to the first and secondelectrodes as the modulated electrical signal.

Packet-Based Modulation

FIG. 12 is a graph illustrating modulated stimulation waveform accordingto some embodiments of the present invention. Referring to FIG. 12, awaveform may include a plurality of spaced-apart packets of pulses. Thepulses may correspond to electrical pulses produced based on thewaveform.

Ones of the plurality of packets may include a quantity, N, of pulsesand a separation in time, S, between adjacent ones of the plurality ofpackets of pulses. For example, as illustrated in FIG. 12, the packetsmay each include a quantity, N, of 3 pulses, although the presentinvention is not limited thereto. For example, the quantity, N, ofpulses may be more or less than three but, in some embodiments, may beat least 2. The separation in time, S, between adjacent ones of theplurality of packets may be defined as a quantity of time between an endof a last pulse of one packet and a beginning of the first pulse of thenext adjacent packet.

Ones of the pulses may include a width in time, W, an amplitude, A, anda separation in time, X, between adjacent ones of the pulses within apacket. The width in time, W, of a pulse may be defined as a quantity oftime between a rising edge and a falling edge of a single pulse,although the present invention is not limited thereto. The amplitude, A,of the waveform may correspond to the amplitude of the voltage of theelectrical signal provided by the electrode 215 of FIG. 8. Theseparation in time, X, between adjacent ones of the pulses within apacket may be defined as a quantity of time between an end of one pulsewithin a packet and a beginning of the next pulse within the samepacket.

An impedance provided by the skin of FIG. 8 in response to an electricalsignal corresponding to the stimulation waveform may be based on thewidth in time, W, of the pulses and the separation in time, X, betweenadjacent ones of the pulses within a packet. For example, the width, W,and separation, X, may define a time period of a pulse. A frequency ofthe pulses may be the inverse of the time period. The impedance may beinversely proportional to the frequency of the pulses, as illustrated inFIG. 11. Thus, the width, W, and separation, X, may be selected to besmaller to provide a higher frequency and, thus, a lower impedance.

At least one of the quantity, N, of the plurality of pulses within onesof the plurality of packets of pulses, the width in time, W, of theplurality of electrical pulses within ones of the plurality of packetsof pulses, the amplitude, A, of the plurality of pulses within ones ofthe plurality of packets of pulses, the separation in time, X, betweenadjacent ones of the plurality of pulses within ones of the plurality ofpackets of pulses, and the separation in time, S, between adjacent onesof the plurality of packets of pulses may be modulated to modulate thestimulation waveform. The at least one modulated parameter may bemodulated based on a target stimulus frequency. Referring to FIGS. 8 and10, the vestibular system may be stimulated based on the target stimulusfrequency. Thus, the target stimulus frequency may be selected to be lowbased on the desired diagnostic and/or therapeutic uses of the galvanicvestibular stimulation.

In some embodiments, the separation in time, S, between adjacent ones ofthe plurality of packets of pulses may be modulated to modulate thestimulation waveform. In other words, the separation in time, S, may notbe constant and may be varied based on the target stimulus frequency.For example, the separation in time, Si between the first packet and thesecond packet illustrated in FIG. 12 may be different from theseparation in time, S2 between the second packet and the third packetillustrated in FIG. 12.

FIG. 13 is a graph illustrating a modulated separation in time betweenadjacent ones of a plurality of packets of electrical pulses accordingto some embodiments of the present invention. Referring to FIGS. 12 and13, the separation in time, S, between adjacent ones of the plurality ofpackets of pulses may be varied in a sinusoidal modulation. Theseparation in time, S, may vary between a minimum separation value and amaximum separation value. A period of the sinusoidal modulation maydefine the stimulation frequency. For example, a duration in timebetween minimum values or between maximum values may define the period.The stimulation frequency may be defined as the inverse of the period.Thus, the separation in time, S, may be varied in a sinusoidalmodulation to stimulate the vestibular system based on the targetstimulation frequency.

Target neurons of the vestibular system may require a minimum amount oftime after stimulation to recover. The target neurons may be stimulatedby each pulse. Because the separation in time, X, between pulses withina packet may be selected to be small to provide decreased impedance, thetarget neurons may not recover between pulses within a packet. Thus, thetarget neurons may be constantly stimulated within a duration of apacket of pulses. However, the minimum value of the separation in time,S, between packets may be selected to be sufficiently large to allowtarget neurons to recover before being activated by the next packet ofpulses. Thus, by modulating the separation in time, S, the stimulationof the target neurons may be modulated based on the target stimulusfrequency. See, e.g., M. W. Bagnall, L. E. McElvain, M. Faulstich, S. duLac, Frequency-independent synaptic transmission supports a linearvestibular behavior. Neuron 60, 343-352 (2008); published online EpubOct23 (S0896-6273(08)00845-3 [pii]10.1016/j.neuron.2008.10.002) (discussingrecovery of vestibular afferent synapse after stimulus trains).

The galvanic vestibular stimulation may have downstream effects in otherportions of the brain of the subject based on the target stimulusfrequency. In some embodiments, a frequency of the modulated signal maybe selected to induce brain rhythms in a target portion of the brain. Insome embodiments, the galvanic vestibular stimulation may entrainendogenous brain rhythms in a target portion of the brain based on themodulated signal.

In some embodiments, the separation in time, S, may be varied accordingto the formula S(t)=S_(min)+S_(c)*sin(ωt), wherein S(t) is theseparation in time, S, between adjacent ones of the plurality of packetsof electrical pulses, S_(min) and S_(c) are time constants, and ω isproportional to the target stimulus frequency. However, embodiments ofthe present invention are not limited thereto. For example, in someembodiments, the separation in time, S, may be varied according to otherformulas, such as S(t)=S_(min)+S_(c)*cos(ωt). Without wishing to bebound by any particular theory, it is believed that an amplitude of theseparation in time, S, may be inversely proportional to an amplitude ofan induced stimulus. For example, with a reduced separation in time, S,a vestibular system will receive more packets of electrical pulseswithin a given time. Conversely, with an increased separation in time,S, the vestibular system will receive fewer packets of electrical pulseswithin the given time. By modulating the separation in time, S, anamplitude of the induced stimulus may therefore be modulated. Thus, bymodulating the separation in time, S, according to a target frequency,the induced stimulus may therefore be modulated according to the targetfrequency. Accordingly, brainwaves may be entrained according to thestimulus frequency.

FIG. 14 is a graph illustrating a modulated separation in time betweenadjacent ones of a plurality of packets of electrical pulses and acorresponding modulated stimulation waveform according to someembodiments of the present invention. Referring to FIG. 14, a separationof time, S, between adjacent ones of a plurality of packets of pulses isillustrated as varied in a sinusoidal modulation. An amplitude of awaveform is illustrated corresponding to the modulation of S. Forexample, a longer separation in time is illustrated between adjacentpackets when S is higher and a shorter separation in time is illustratedwhen S is lower. In the illustrated example, each of the packetsincludes three pulses of equal amplitude, width, and separation, howeverembodiments are not limited thereto.

FIGS. 15A, 15C, and 15E are graphs illustrating modulated targetstimulus frequencies according to some embodiments of the presentinvention. FIGS. 15B, 15D, and 15F are graphs illustrating modulatedseparations in time between adjacent ones of a plurality of packets ofelectrical pulses according to the modulated target stimulus frequenciesof FIGS. 15A, 15C, and 15E, respectively. Referring to FIGS. 12-13 and15A-15F, in some embodiments, the formula may include more than onetarget stimulus frequency. For example, in some embodiments, the formulamay include a range of frequencies. In some embodiments, the modulatingmay include modulating the target stimulus frequency between a lowertarget frequency and a higher target frequency.

Referring to FIGS. 15A-15B, in some embodiments, the modulating mayinclude repeatedly decreasing the target stimulus frequency in a patternbetween the higher target frequency and the lower target frequency. Aperiod of the sinusoidal modulation of the separation in time, S, mayincrease over time as the target frequency decreases. The patternsillustrated in FIGS. 15A-15B may be consecutively repeated for aduration of the galvanic vestibular stimulation.

Referring to FIGS. 15C-15D, in some embodiments, the modulating mayinclude repeatedly increasing the target stimulus frequency in a patternbetween the lower target frequency and the higher target frequency. Aperiod of the sinusoidal modulation of the separation in time, S, maydecrease over time as the target frequency increases. The patternsillustrated in FIGS. 15C-15D may be consecutively repeated for aduration of the galvanic vestibular stimulation.

Referring to FIGS. 15E-15F, in some embodiments, the modulating mayinclude repeatedly cycling the target stimulus frequency in a pattern ofincreasing from the lower target frequency to the higher targetfrequency and then decreasing back to the lower target frequency. Aperiod of the sinusoidal modulation of the separation in time, S, maydecrease over time as the target frequency increases and may increase asthe target frequency decreases. The patterns illustrated in FIGS.15E-15F may be consecutively repeated for a duration of the galvanicvestibular stimulation.

Carrier-Based Modulation

FIGS. 16A-D are graphs illustrating a method for modulating anelectrical signal according to some embodiments of the presentinvention. For example, FIG. 16A is a graph illustrating a carrierwaveform function according to some embodiments of the presentinvention, FIG. 16B is a graph illustrating a modulation waveformaccording to some embodiments of the present invention, FIG. 16C is agraph illustrating an amplitude modulated electrical signal according tosome embodiments of the present invention, and FIG. 16D is a graphillustrating a frequency modulated electrical signal according to someembodiments of the present invention. Referring to FIG. 16A, a carrierwaveform function may be a continuous cyclical function. For example, insome embodiments, the carrier waveform function may be a sine wave. Insome embodiments, the carrier waveform function may be a square wave, asawtooth wave, or another waveform function. The carrier waveformfunction may include an amplitude and a carrier frequency. The carrierwaveform function may include a sequence of pulses that may correspondto electrical pulses produced based on the function.

Ones of the pulses may include a width in time, W and an amplitude, A.The width in time, W, of a pulse may be defined as a quantity of timebetween corresponding phases of adjacent pulses. The amplitude, A, ofthe waveform may correspond to the amplitude of the voltage and/orcurrent of the electrical signal provided by the electrode 215 of FIG.8.

An impedance provided by the skin as shown in FIG. 8 in response to anelectrical signal corresponding to the carrier waveform function may bebased on the width in time, W, of the pulses. For example, the width, W,may define a time period of a pulse. A carrier frequency of the carrierwaveform function may be the inverse of the time period. The impedancemay be inversely proportional to the frequency of the pulses, asillustrated in FIG. 11. Thus, the width, W, may be selected to besmaller to provide a higher frequency and, thus, a lower impedance. Forexample, in some embodiments, the carrier frequency may be greater thanabout 3 kHz. In some embodiments, the carrier frequency may be about 10kHz.

Referring to FIGS. 16A-16D, at least one of the amplitude, A, and thecarrier frequency may be modulated to modulate a stimulation waveform.The at least one modulated parameter may be modulated based on amodulation waveform. For example, referring to FIGS. 16A-16C, theamplitude of the carrier waveform function may be modulated based on themodulation waveform to produce an amplitude modulated electrical signal.Referring to FIGS. 16A-16B and FIG. 16D, the frequency of the carrierwaveform function may be modulated based on the modulation waveform toproduce a frequency modulated electrical signal. In some embodiments,the modulation waveform may be a sinusoidal function. In suchembodiments, the amplitude and/or frequency of the carrier waveformfunction may be varied in a sinusoidal modulation. However, in otherembodiments, the modulation waveform may not be sinusoidal and may beanother waveform. Referring to FIGS. 8 and 10, the vestibular system maybe stimulated based on the modulation frequency. Thus, the modulationfrequency may be selected to be low based on the desired diagnosticand/or therapeutic uses of the galvanic vestibular stimulation. In someembodiments, the modulation frequency may be less than about 1 kHz. Forexample, in some embodiments, the modulation frequency may be betweenabout 0.005 Hz and about 200 Hz. However, in some embodiments, amodulation frequency that is greater than 1 kHz may be selected based onanother desired diagnostic and/or therapeutic use of the galvanicvestibular stimulation.

The galvanic vestibular stimulation may have downstream effects in otherportions of the brain of the subject based on the modulation frequency.In some embodiments, a frequency of the modulated signal may be selectedto induce brain rhythms in a target portion of the brain. In someembodiments, the galvanic vestibular stimulation may entrain endogenousbrain rhythms in a target portion of the brain based on the modulatedsignal.

In some embodiments, the modulation waveform may include more than onemodulation frequency. For example, in some embodiments, the modulationwaveform may include a range of frequencies. In some embodiments, themodulating may include modulating the modulation waveform between alower target frequency and a higher target frequency. In someembodiments, the modulating may include repeatedly decreasing themodulation frequency in a pattern between the higher target frequencyand the lower target frequency. In some embodiments, the modulating mayinclude repeatedly increasing the modulation frequency in a patternbetween the lower target frequency and the higher target frequency. Insome embodiments, the modulating may include repeatedly cycling themodulation frequency in a pattern of increasing from the lower targetfrequency to the higher target frequency and then decreasing back to thelower target frequency.

Applications

Embodiments according to the present invention will now be describedwith respect to the following non-limiting examples

Alteration of Cross-Frequency Coupling

The oscillatory activity in multiple frequency bands may be observed indifferent levels of organization from micro-scale to meso-scale andmacro-scale. Studies have been shown that some brain functions areachieved with simultaneous oscillations in different frequency bands.The relation and interaction between oscillations in different bands canbe informative in understanding brain function. This interaction betweenseveral oscillations is also known as cross-frequency coupling (CFC).

Two forms of recognized CFC in brain rhythms are: phase amplitudecoupling (PAC), and phase-phase coupling (PPC). In phase amplitudecoupling, the phase of the lower frequency oscillation may drive thepower of the coupled higher frequency oscillation, which may result insynchronization of amplitude envelope of faster rhythms with the phaseof slower rhythms. Phase-phase coupling is amplitude independent phaselocking between high and low frequency oscillation.

It is believed that phase-amplitude coupling may be a mechanism forcommunication within and between distinct regions of the brain bycoordinating the timing of neuronal activity in brain networks. Thatbrain rhythms modulate the excitability of neuronal ensembles throughfluctuations in membrane potentials, biasing the probability of neuronalspiking at a specific phase of the slower rhythm. PAC is thought todynamically link functionally related cortical areas that are essentialfor task performance.

Parkinson's disease (PD) has been shown to be associated withexaggerated coupling between the phase of beta oscillations and theamplitude of broadband activity in the primary motor cortex, likelyconstraining cortical neuronal activity in an inflexible pattern whoseconsequence is bradykinesia and rigidity. See, e.g., C. de Hemptinne, N.C. Swann, J. L. Ostrem, E. S. Ryapolova-Webb, M. San Luciano, N. B.Galifianakis, P. A. Starr, Therapeutic deep brain stimulation reducescortical phase-amplitude coupling in Parkinson's disease, Nat Neurosci18, 779-786 (2015); published online EpubApr 13 (10.1038/nn.3997).Parkinson's disease may be associated with a range of symptoms thatoriginate, or are centered, in different brain regions. It is believedthat aberrant cross-frequency coupling between two different EEG bandsmay be present when a patient experiences tremor. It is believed thatCVS and/or GVS may be used to alter the cross-frequency coupling so asto renormalize function and re-establish proper balance.

Stimulation of a region in the brain stem called the PPN has been shownto improve, for example, the normalization of gait in PD patients. See,e.g., H. Morita, C. J. Hass, E. Moro, A. Sudhyadhom, R. Kumar, M. S.Okun, Pedunculopontine Nucleus Stimulation: Where are We Now and WhatNeeds to be Done to Move the Field Forward? Front Neurol 5, 243 (2014);published online (10.3389/fneur.2014.00243). With respect to the presentinvention, without wishing to be bound by theory, it is believed thatvestibular stimulation may modulate activity of the PPN. For example,CVS may be used to stimulate the PPN. In some embodiments, GVS may beused to break up the aberrant cross frequency coupling associated withtremor simultaneous with the use of CVS to stimulate the PPN. Thus, thetwo modalities may modulate different brain regions to improve theefficacy of the treatment.

More generally, GVS may be used to sensitize or give preference to asubset of neural pathways that respond to a specific excitationfrequency (for example, within the EEG bands), making them moreresponsive to CVS neuromodulation. These selected pathways would then besubject to differential modulation in the background of other,non-selected pathways. An illustrative example would be the use of GVSin the theta band frequency range, associated with hippocampal activity,to sensitize pathways associated with memory encoding. GVS at asub-threshold intensity may be used, or the intensity may be above theactivation threshold of the afferent vestibular nerves. The CVS waveformwould be chosen so as to overlap and enhance the neuromodulatory effectsof the targeted GVS modulation.

Controlling IGF-1 Accretion

Insulin-like growth factor 1 (IGF-1) is a hormone that is similar inmolecular structure to insulin that is believed to play an importantrole in childhood growth and to have anabolic effects in adults. Theprotein is encoded in humans by the IGF1 gene. It is believed that IGF-1may also provide mitochondrial protection

Insulin-like growth factor number one (IGF-1) is a hormone (MW: 7649daltons) similar in molecular structure to insulin. It plays animportant role in childhood growth and continues to have anaboliceffects in adults. Its production is encoded by the IGF1 gene and it isproduced primarily in the liver as an endocrine hormone, thoughproduction in the central nervous system has also been observed. Incirculation, IGF-1 is bound to one of six proteins, the most commonbeing IGFBP-3. These chaperone proteins increase the half life of IGF-1in circulation from around 15 minutes (unbound) to 15 hours (bound).IGF-1 production is associated with growth hormone (GH) and blood testsfor GH use IGF-1 as a surrogate, since the concentration of the lattertends not to vary as much over a daily cycle as that of GH does. IGF-1is one of the most potent natural activators of the AKT signalingpathway, a stimulator of cell growth and proliferation, and a potentinhibitor of programmed cell death. It protects and strengthens cells atone of their most vulnerable moments, when they are in the process ofand immediately after dividing. It is believed that IGF-1 may providemitochondrial protection from mitochondrial stress.

Electrical stimulation of the fastigial nucleus (FN) for a sufficienttime and at the right frequency has been shown to lead toneuroprotection via reduction of apoptosis in mitochondria in theischemic area. See, e.g., P. Zhou, L. Qian, T. Zhou, C. ladecola,Mitochondria are involved in the neurogenic neuroprotection conferred bystimulation of cerebellar fastigial nucleus, J. Neurochem 95, 221-229(2005). It is believed that IGF-1 may be a factor in suchneuroprotection. Electrical stimulation has been shown to result in therecruitment of IGF-1 from systemic circulation, through theblood-brain-barrier, and to very localized usage by or around the pointof the stimulated nerves. Effectively, the nerve activity signaled forand recruited IGF-1. See, e.g., T. Nishijima, J. Piriz, S. Duflot, A. M.Fernandez, G. Gaitan, U. Gomez-Pinedo, J. M. Verdugo, F. Leroy, H. Soya,A. Nunez, I. Torres-Aleman, Neuronal activity drives localizedblood-brain-barrier transport of serum insulin-like growth factor-I intothe CNS, Neuron 67, 834-846 (2010). It is believed that vestibularstimulation may similarly accomplish the recruitment of and/or enhancethe efficiency of IGF-1, either directly affecting nerves active duringvestibular stimulation or possibly nearby nerves receive IGF-1 in abystander effect. For migraine headache in particular, increased rCBFmay be a key factor enabling increased IGF-1 uptake through the BBB.Mechanisms for altering blood flow mesh nicely with existingobservations/beliefs around the etiology of migraines. That IGF-1 alsofacilitates synaptic plasticity could mean it has a role in mitigatingcentral pain associated with chronic migraines.

With respect to the present invention, without wishing to be bound bytheory, it is believed that vestibular stimulation, or in particular CVSand/or GVS, may be used to increase IGF-1 transport across theblood-brain-barrier, and therefore increase mitochondrial protection, infrequency-dependent targeted regions of the central nervous system. Insome embodiments, CVS and GVS may be combined. For example, CVS may beused to provide stimulation of frequency-dependent regions of the brainand GVS may be used to provide neuroprotection to the stimulated regionsand/or surrounding regions.

Although embodiments have been described with reference to galvanicvestibular stimulation through an ear canal, the present inventiveconcepts are not limited thereto. For example, in some embodiments, thevestibular system may be stimulated through at least one electrode incontact with a portion of the skin behind the ear in proximity to amastoid part of a temporal bone. In some embodiments, delivering theelectrical signal may include transdermal electrical stimulation ofother portions of a nervous system of the subject. In some embodiments,the described modulation scheme may be used with implantable electrodesor other devices that do not stimulate through the skin.

The foregoing is illustrative of the present invention and is not to beconstrued as limiting thereof. Although a few exemplary embodiments ofthis invention have been described, those skilled in the art willreadily appreciate that many modifications are possible in the exemplaryembodiments without materially departing from the novel teachings andadvantages of this invention. Accordingly, all such modifications areintended to be included within the scope of this invention as defined inthe claims. Therefore, it is to be understood that the foregoing isillustrative of the present invention and is not to be construed aslimited to the specific embodiments disclosed, and that modifications tothe disclosed embodiments, as well as other embodiments, are intended tobe included within the scope of the appended claims. The invention isdefined by the following claims, with equivalents of the claims to beincluded therein.

That which is claimed is:
 1. A method of neurostimulation, comprising:delivering an electrical signal to a plurality of electrodes connectedto a patient, the electrical signal comprising a plurality of packets ofelectrical pulses spaced apart from each other by a second separation intime between adjacent packets of electrical pulses, each of theplurality of packets of electrical pulses comprising a plurality ofelectrical pulses spaced apart from each other by a first separation intime between adjacent electrical pulses within each packet, and eachelectrical pulse comprising a width in time and an amplitude in voltage;and modulating the second separation in time between the packets ofelectrical pulses based on a target stimulus frequency by varying thefirst separation in time in a sinusoidal modulation in a range betweenabout 100 microseconds and about 100 milliseconds to modulate thedelivered electrical signal based on a time-varying modulation waveform.2. The method of claim 1, wherein the modulating comprises: modulating aquantity of the plurality of electrical pulses within ones of theplurality of packets of electrical pulses based on the target stimulusfrequency.
 3. The method of claim 1, wherein the modulating comprises:modulating the width in time of the plurality of electrical pulseswithin ones of the plurality of packets of electrical pulses based onthe target stimulus frequency.
 4. The method of claim 1, wherein themodulating comprises: modulating the amplitude in voltage of theplurality of electrical pulses within ones of the plurality of packetsof electrical pulses based on a target stimulus frequency.
 5. The methodof claim 1, wherein the modulating comprises: modulating the firstseparation in time between adjacent ones of the plurality of electricalpulses within ones of the plurality of packets of electrical pulsesbased on the target stimulus frequency.
 6. The method of claim 1,wherein the modulating comprises: varying the first separation in timebetween adjacent ones of the plurality of packets of electrical pulsesin a sinusoidal modulation between a minimum value and a maximum valuebased on the target stimulus frequency.
 7. The method of claim 6,wherein the minimum value of the first separation in time betweenadjacent ones of the plurality of packets of electrical pulses isconfigured to allow target neurons to recover before being activated bya subsequent packet of electrical pulses of the adjacent ones of theplurality of packets of electrical pulses.
 8. The method of claim 6,wherein the varying comprises: varying the first separation in timebetween adjacent ones of the plurality of packets of electrical pulsesaccording to a formula S(t)=S_(min)+S_(c)*sin(ωt), wherein S(t) is thefirst separation in time between adjacent ones of the plurality ofpackets of electrical pulses, S_(min) and S_(c) are time constants, andω is proportional to the target stimulus frequency.
 9. The method ofclaim 1, wherein modulating the electrical signal comprises selectingcharacteristics of electrical signal to modulate so as to induce brainrhythms in a target portion of a brain of the patient based on themodulated delivered electrical signal.
 10. The method of claim 1,further comprising: entraining endogenous brain rhythms in a targetportion of a brain of the patient based on the modulated deliveredelectrical signal.
 11. The method of claim 1, wherein modulatingcomprises: modulating the target stimulus frequency between a lowertarget frequency and a higher target frequency.
 12. The method of claim1, wherein delivering the electrical signal comprises delivering theelectrical signal via transdermal electrical stimulation.
 13. The methodof claim 1, wherein delivering the electrical signal comprisesdelivering the electrical signal via galvanic vestibular stimulation(GVS).
 14. The method of claim 1, further comprising: selecting thetime-varying modulation waveform to reduce symptoms of Parkinson'sdisease.
 15. The method of claim 1, further comprising: selecting thetime-varying modulation waveform to reduce symptoms of migraineheadache.
 16. A neurostimulation device, comprising: first and secondelectrodes; and a controller comprising a waveform generator configuredto deliver a modulated electrical signal to a subject through the firstand second electrodes, the modulated electrical signal comprising aplurality of packets of electrical pulses spaced apart from each otherby a second separation in time between adjacent packets of electricalpulses, each of the plurality of packets of electrical pulses comprisinga plurality of electrical pulses spaced apart from each other by a firstseparation in time between adjacent electrical pulses within eachpacket, each electrical pulse comprising a width in time and anamplitude in voltage; wherein the controller is configured to modulatethe delivered electrical signal by varying the second separation in timebetween adjacent ones of the plurality of packets of electrical pulsesbased on a time-varying modulation waveform and based on a targetstimulus frequency by varying the second separation in time in asinusoidal modulation in a range between about 100 microseconds andabout 100 milliseconds.
 17. The neurostimulation device of claim 16,wherein the first and second electrodes are configured to deliver themodulated electrical signal to the subject through transdermal galvanicvestibular stimulation (GVS).
 18. The neurostimulation device of claim16, wherein the controller is configured to vary the first separation intime between adjacent ones of the plurality of packets of electricalpulses in a sinusoidal modulation between a minimum value and a maximumvalue based on the target stimulus frequency.
 19. The neurostimulationdevice of claim 18, wherein the minimum value of the first separation intime between adjacent ones of the plurality of packets of electricalpulses is configured to allow target neurons to recover before beingactivated by a subsequent packet of electrical pulses of the adjacentones of the plurality of packets of electrical pulses.
 20. Theneurostimulation device of claim 16, wherein the controller isconfigured to vary the first separation in time between adjacent ones ofthe plurality of packets of electrical pulses according to a formulaS(t)=S_(min)+S_(c)*sin(ωt), and wherein S(t) is the first separation intime between adjacent ones of the plurality of packets of electricalpulses, S_(min) and S_(c) are time constants, and ω is proportional tothe target stimulus frequency.